Monofilament, Surgical Mesh Having Improved Flexibility and Biocompatibility, and Process for Preparing the Same

ABSTRACT

The present invention relates to a monofilament with a segmented pie structure formed by conjugated spinning of degradable polymers and non-degradable polymers, a hernia mesh having improved flexibility and biocompatibility, and a preparation method thereof. More specifically, the hernia mesh of the present invention having improved flexibility and biocompatibility is prepared using the monofilament obtained by conjugated spinning of degradable polymers and non-degradable polymers into a segmented pie form, to control it to be gradually degraded in the body, whereby the stiffness of the early stage is removed, and thereby the foreign body sensation is also removed.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a monofilament having a segmented piestructure formed by conjugated spinning of degradable polymers andnon-degradable polymers, a hernia mesh comprising the monofilamenthaving improved flexibility and biocompatibility, and a method forpreparing the same. More specifically, the present invention relates toa monofilament prepared by conjugated spinning of degradable polymersand non-degradable polymers in the form of a segmented pie; a herniamesh that is prepared with the monofilament and that is controlled to begradually degraded in the body while losing the stiffness of the earlystage, causing no misfeelings, and having improved flexibility andbiocompatibility; and a method of preparation thereof.

(b) Description of the Related Art

Tension-free hernioplasty (Lichtenstein I L, Am J Surg 1989; 157;188-193) is considered to be a useful method for reparation of hernias,because the relapse ratio thereafter is low, the operative time isshort, and the operative wound heals quickly, and thereby the patientcan rapidly return to normal life. Conventionally, since the mesh usedfor hernia repair is required to have the capability of maintaining itschemical and physical properties for several years to strengthen theperitoneum, polypropylene monofilaments have been used as the materialfor a hernia mesh. However, it has been reported that the polypropylenemesh may have the potential to generate fistulas in the intestine(Seelig M H, “A rare complication after incisional hernia repair”.Chirurg 1995; 66(7); 739-741, Leber G E, “Long-term complicationsassociated with prosthetic repair of incisional hernias”, Arch Surg1988; 133(4); 378-382). Further, as general side effects of thepolypropylene mesh, an edema, a restriction of abdominal wall mobilitydue to stiffness of the peritoneum where the artificial membrane islocated and pain from misfeelings caused by the stiffness, a chronicinflammatory response between the polypropylene fibers and tissues inbody, and the like have been reported (Amid P K, “Biomaterials forabdominal wall hernia surgery and principles of their applications”,Lagenbecks Arch Chir 1994; 379(3): 168-171, Waldrep D J, “Mature fibrouscyst formation after Marlex Vestweber K, Results of recurrent abdominalwall hernia repair using polypropylene mesh”. Zentralblatt Für Chirurgie1997; 122:885-8, Bellon J M, “Integration of biomaterials implanted intoabdominal wall: mesh ventral herniorrhaphy: a newly described pathologicentity”. Am Surg 1993; 59(11):716-8, “Process of scar formation andmacrophage response”. Biomaterials 1995; 16(5):381-7, Klinge U, “Changesin abdominal wall mechanics after mesh implantation”. Experimentalchanges in mesh stability. Lagenbecks Arch Chir 1996; 381(6): 323-32).

The hernia mesh needs stiffness in order to be positioned and fixed onthe surgical wound region when performing the surgical operation. Forthat purpose, several methods to prepare the hernia mesh using fibers inthe monofilament form have been known. U.S. Pat. No. 4,347,847, U.S.Pat. No. 4,452,245, U.S. Pat. No. 5,569,273, and U.S. Pat. No. 6,287,316disclose a method to prepare a hernia mesh consisting of polypropylenemonofilaments. However, since polypropylene is non-degradable, afterperforming the surgical operation using the hernia mesh, the strengthand stiffness of the mesh that are necessary during the initial stageafter the surgical operation are continuously maintained in the body.Therefore, the mesh has excessive stiffness even after the wound hashealed, causing pain to the patient due to misfeelings. Further, U.S.Pat. No. 5,292,328 discloses a method of preparing a hernia meshconsisting of polypropylene multifilaments in order to improve theflexibility, in which the mesh has a somewhat improved initialflexibility compared with that consisting of the monofilaments. However,since the mesh consists of only non-degradable materials, there are alsosome problems in that the initial strength and stiffness of the mesh arecontinuously maintained in the body, and an excessive amount ofpolypropylene remains in the body. To solve these problems, studies ondevelopment of a partially degradable mesh wherein the content ofpolypropylene is decreased and the strength and stiffness necessary forthe initial stage is supplemented by additionally comprising degradablematerials, have been disclosed in U.S. Pat. No. 4,652,264 and U.S. Pat.No. 6,162,962. Herein, the degradable materials are partially degradedafter the wound has healed, to improve the flexibility of the mesh. U.S.Pat. No. 4,652,264 discloses a method to prepare a mesh by combiningthreads consisting of three different materials, of which two aredegradable and one is non-degradable. U.S. Pat. No. 6,287,316 disclosesa method of preparing a mesh using a multifilament consisting ofdegradable materials and non-degradable materials. However, since themeshes prepared by the above methods consist of several threads ofdegradable and non-degradable materials in the combined form, there is apossibility of bacterial infection within the spaces between thethreads, which is an inherent defect of multifilaments. Further, sincethe methods employ the multifilament form wherein several strands offiber are combined, the amount of materials required for exhibiting thenecessary stiffness is larger than the case of using the monofilament.In addition, the multifilament causes a strong foreign body response dueto the large surface area (Beets G L, “Foreign body reactions tomonofilament and braided polypropylene mesh used as preperitonealimplants in pigs”. Eur J Surg 1996; 162:823-825).

As known from the above prior art, although the use of a hernia mesh hasbeen regarded as a basic means in performing hernia repairs, there areunsatisfactory results obtained from the studies to develop a herniamesh for improving the convenience in performing the operation, reducingthe misfeelings, and having improved biocompatibility. Therefore, it isrequired to develop a hernia mesh that can maintain its strength andstiffness at the early stage, thereby ensuring convenience in performingthe operation, and be partially degraded as the surgical wound ishealed, thereby improving the flexibility of the remaining mesh.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a monofilament havinga segmented pie structure formed by conjugated spinning of degradablepolymers and non-degradable polymers.

Another object of the present invention is to provide a hernia surgicalmesh comprising the monofilament, having improved flexibility andbiocompatibility.

Another object of the present invention is to provide a method ofpreparing the hernia mesh.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A is an optical microscopic image of a cross section of theconjugated filament in the segmented pie form according to the presentinvention [1: degradable polymer, 2: non-degradable polymer].

FIG. 1B is a SEM (scanning electron microscope) image of the crosssection of the conjugated filament in the segmented pie form accordingto the present invention.

FIG. 2A is a SEM image prior to degradation of the mesh prepared withthe monofilament obtained by conjugated spinning.

FIG. 2B is a SEM image after degradation of the mesh prepared with themonofilament obtained by conjugated spinning.

FIG. 3A is a SEM image of the cross section of the monofilament preparedby conjugated spinning using 75 volume % of degradable materials.

FIG. 3B is a SEM image showing a distortion of the monofilament in thesegmented pie form when the difference between the melt indexes is morethan 14 in conjugated spinning.

FIG. 3C is an SEM image showing fiber separation when thestress-relaxation is not performed under the drawing conditions inconjugated spinning.

FIG. 4 is a schematic diagram showing the flow of two polymers at adistributing plate and a nozzle in the conjugated spinning apparatus forpreparing the monofilament in the segmented pie form.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventors have conducted continued studies to develop anovel hernia mesh with partial degradability, which maintains itsstrength and stiffness at the early stage to secure convenience inperforming a surgical operation and then becomes partially degradedduring healing of the surgical wound to increase the flexibility of themesh remaining in the body, resulting in alleviating the patient's painand improving the biocompatibility by remarkably reducing the amount ofnon-degradable materials used. As the result, the present inventorsfound that when preparing a monofilament in the segmented pie form byconjugated spinning of degradable polymers and non-degradable polymers,the strength and stiffness necessary for the early stage of the surgicaloperation can be achieved by the stiffness characteristic of themonofilament itself, and after performing the operation, themonofilament becomes partially degraded in the body, and thereby themesh consisting thereof can remain in the body in the more flexiblestructure, to complete the present invention.

Hereinafter, the present invention will be described in detail.

The present invention relates to a hernia mesh with improved flexibilityand biocompatibility and a preparation method thereof, wherein the meshcomprises monofilaments having the segmented pie structure formed byconjugated spinning of degradable polymers and non-degradable polymers,being controlled to be gradually degraded in the body, to remove theinitial stiffness of the mesh and to avoid misfeelings due to theremaining mesh.

The monofilament in the segmented pie form, which composes the herniamesh of the present invention, consists of a degradable polymer and anon-degradable polymer, wherein the non-degradable polymer (2) isseparated into several partitions by the degradable polymer (1), and thedegradable polymer (1) has a continuous form [see FIG. 1A]. Themonofilament in the segmented pie form of the present invention ispresent in the monofilament form before degradation, and then, as thedegradable polymer becomes degraded, the monofilament is divided intoindividual strands as a multifilament form, to exhibit improvedflexibility.

The degradable polymer used in the present invention may be ahomopolymer or a copolymer comprising one or more selected from thegroup consisting of glycolide, glycolic acid, lactide, lactic acid,caprolactone (ε-caprolactone), dioxanone (p-dioxanone),trimethylenecarbonate, polyanhydride, and polyhydroxyalkanoate, and ismore preferably a glycolide/caprolactone copolymer or adioxanone/trimethylenecarbonate/caprolactone copolymer.

The non-degradable polymer used in the present invention may be selectedfrom the group consisting of polyolefins such as polypropylene,polyethylene, and a copolymer of propylene and ethylene; polyamides suchas nylon 6 and nylon 66; polyurethanes; and fluoropolymers such aspolyvinylidene fluoride, and is more preferably polypropylene or acopolymer of propylene and ethylene.

In particular, the content of the degradable polymer is preferably 30 to70 vol % and the content of the non-degradable polymer is preferably 30to 70 vol %, and more preferably, the content of the degradable polymeris 40 to 60 vol % and the content of the non-degradable polymer is 40 to60 vol %. When the content of the degradable polymer is less than 30 vol%, in spinning, the volume of the degradable polymer is too small toseparate the non-degradable polymer, and thus the non-degradable polymeris in the continuously linked form. When the content of thenon-degradable polymer is less than 30 vol %, the remaining amount ofthe non-degradable polymer after degradation is too low to maintainminimum strength, and further, the monofilament may be prepared in asea/islands type wherein the non-degradable polymer is surrounded by thedegradable polymer as shown in FIG. 3A.

The monofilament prepared by conjugated spinning may be divided intoseveral types, such as sea/islands type, a segmented pie type, aside-by-side type, a sheath/core type, and the like, depending on thestructures, and the preferable type in the present invention is thesegmented pie type. The segmented pie type has some advantages in thatthe degradable materials and the non-degradable materials are uniformlyspread on the surface of the fibers to attain the mobility of theperitoneum by an appropriate combination of fat tissue formed around thedegradable material and connective tissue appeared around thenon-degradable material, and to improve the adhesive property betweenthe mesh and the tissues. Further, different from the conjugated yarntype such as the sea/islands type or the sheath/core type whereon thenon-degradable material is surrounded by the degradable material, thesegmented pie type monofilament can connect with the tissues in the bodyat the early stage after the surgical operation, and thus induce strongadhesion between the mesh and the tissues shortly after performing thesurgical operation [U. Klinge, “Influence of polyglactin-coating onfunctional and morphological parameters of polypropylene-meshmodifications for abdominal wall repair”, Biomaterials 1999;20:613-623,U. Klinge, “Foreign body reaction to meshes used for the repair ofabdominal wall” Hernias, Eur J Surg, 1999;1 65:665-673].

In mesh prepared with the segmented pie type monofilament, in order toreduce the stiffness after healing of the surgical wound to less than70% of the initial stiffness and to improve the flexibility of the mesh,it is preferable to divide the non-degradable polymer into at least fourstrands, and more preferably 6 to 10 strands.

In mesh prepared with the sea/islands type or sheath/core type ofmonofilament, the sea or sheath which is an outside component of themonofilament must be composed of the degradable polymer, and the islandor core which is an inside component of the monofilament must becomposed of the non-degradable polymer. In these cases, as thedegradable polymer located at the outside of the monofilament isdegraded and dispersed, the monofilament starts exhibiting an excessivesurface area and excessive fibrosis (capsule formation) occurs, wherebythe strong adhesion between the mesh and the tissues in the body isinhibited. Further, in the side-by-side type of monofilament wherein oneof two components is located at one side of the cross section and theother is located at the other side, the non-degradable polymer causes aninflammatory response, and rigid connective tissue is formed around themesh, inhibiting the mobility of the peritoneum. These types areunsuitable for the object of the present invention which is to improvethe flexibility of the peritoneum, and are difficult to prepare with twocomponents having different melting behaviors and different thermalcontractibility. In addition, since the two components have the samediameter, the diameter of the remaining non-degradable fiber increases,and thereby there is a limitation in improving the flexibility of theremaining mesh.

The diameter of the monofilament may be controlled so as to have thestrength and/or stiffness necessary at the early stage after performingthe surgical operation, and at the same time to prevent a large amountof the non-degradable polymer from remaining in the body, therebyimproving the biocompatibility and the flexibility. That is, in order tomaintain the initial strength and stiffness, it is required for thefiber to have a density and diameter of a certain degree or higher,while in order to minimize a foreign body response when inserted in thebody, it is required that the total amount of fibers used is minimized.In the present invention, the diameter of the monofilament is preferably100 to 250 μm.

The mesh of the present invention may be prepared in various shapes, andis preferably prepared as a net-structure such as a square, hexagonal,or network shape. The density of the mesh is preferably 8 to 20gauges/inch based on the distance between the needles in a flat warpknitting machine. When the mesh is cut in a suitable size and shape forthe surgical wound region of a patient and is applied to the woundregion, problems such as material particles or an unraveling phenomenonmay occur at the edge of the cut-off mesh. Therefore, a structure thatreadily generates particles or an unraveling phenomenon when cut may berelatively undesirable, and the net-structure such as the square,hexagonal, or network may be desirable in view of lesser particlegeneration when cut.

In the present invention, the pore size of the mesh may be 0.1 to 4.0mm, preferably 2.0 to 3.0 mm, and the thickness of the mesh may be 200to 800 μm, preferably 500 to 600 μm.

In the hernia mesh of the present invention, it is preferable that thenon-degradable polymer is partitioned by the degradable polymer, andthat the degradable polymer is continuously linked. The presentinvention provides a method of preparing the monofilament in thesegmented pie structure formed by conjugated spinning of the degradablepolymer and the non-degradable polymer.

In the present invention, to perform spinning, any conventionalconjugated spinning apparatus may be used. In detail, the polymers aremelted by two extruding apparatuses for conjugated spinning. Each of themelted polymers is discharged in a desired amount through eachquantitative pump to control the content ratio of each component. Thepolymers that are melted and passed through the quantitative pump aresubjected to conjugated spinning into one strand of fiber through aconjugated spinning block. FIG. 4 is a schematic diagram of thepreparation of the monofilament in the segmented pie form, showing theflows of the degradable polymer (3) and the non-degradable polymer (4)in the conjugated spinning block. The melted polymer discharged fromeach quantitative pump is gathered at the distributing plate (5) in theconjugated spinning block, and passed through the nozzle to prepare themonofilament in the segmented pie form. The strand obtained byconjugated spinning is solidified and crystallized in a cooling bath.The air gap between the spinnerette and the surface of water in thecooing bath is preferably 0.5 to 100 cm, and more preferably 1 to 30 cm.The solidified fiber is drawn through a multi-stage drawing apparatusand wound in a winder in order to obtain an improvement of the propertyby orientation. A preferable embodiment of the monofilament in thesegmented pie form is shown in FIG. 1A.

To prepare the uniform and stable monofilament in the segmented pie formby spinning process, the melt indexes (MI) of the two polymers and thespinning conditions have to be exactly controlled. The melt index of thedegradable polymer may not be lower than that of the non-degradablepolymer to maintain the segmented pie structure, and the differencebetween the melt indexes of the degradable polymer and thenon-degradable polymer is preferably 10 or less. If the melt index ofthe degradable polymer is lower than that of the non-degradable polymer,the segmented pie structure may be obtained in a distorted and unequalform wherein the distribution of the non-degradable polymer is notequally distributed, being concentrated on a certain position as shownin FIG. 3B. Further, if the difference between the melt indexes of thetwo polymers is more than 10, phase separation easily occurs. Therefore,it is preferable that the melt index of the degradable polymer is notlower than that of the non-degradable polymer, and that the differencebetween the melt indexes of the two polymers is 10 or less.

In addition, when the monofilament in the segmented pie form is preparedby conjugated spinning of two polymers having different properties suchas the melting point, the degree of crystallinity, the thermalcontractibility and the like, improper drawing conditions cause curlingand phase separation of the two components as shown in FIG. 3C. Toprevent such a curling phenomenon, the spinning temperature iscontrolled within a certain range so that the melt index of thedegradable polymer is the same as or higher than that of thenon-degradable polymer, to allow the melting behavior of the twopolymers to form the symmetric structure of the segmented pie form.Further, to prevent the fiber phase separation phenomenon, in a finaldrawing oven, stress relaxation of at least 10% and preferably 10 to 20%is applied in consideration of the thermal contraction rate of the twopolymer components to stabilize the structure.

In order to easily distinguish the mesh when performing the surgicaloperation, the mesh fibers may be dyed at regular intervals. Herein, toprevent the dye from remaining in the body, it is preferable to dye onlythe degradable polymer part. Any dye that is conventionally employed inpreparing sutures, such as D&C violet No.2, D&C Green No.6, FD&C BlueNo.2, and the like, may be used.

The present invention also provides a method for preparing a mesh usingthe above monofilament in the segmented pie form.

In the present invention, the mesh may be prepared through threeconventional steps of warping, knitting, and curing.

In the warping step, several strands are regularly wound on a beam witha constant tension to equally supply a regular amount of fiber beforethe knitting step. Then, the beam is equipped in a flat warp knittingmachine to prepare a mesh. In the present invention, the mesh may beprepared by a Tricot flat warp knitting machine or a Raschel flat warpknitting machine. When preparing the mesh, the texture and shape may becontrolled so as to give the mesh the necessary strength and stiffnessat the early stage and to simultaneously prevent the non-degradablematerials from remaining in the body in a large amount to improve thebiocompatibility and flexibility, controlling the strength and stiffnessof the texture of the mesh. As a final step, the prepared mesh is curedto fix the shape of the mesh. The curing step is performed undertemperature and time conditions such that yellowing and a change of theproperties are avoided. Conventionally, the mesh is cured at atemperature 10° C. to 15° C. lower than the melting point of thecomponent constituting the mesh, e.g., at 90° C. to 160° C., for 1 to 30minutes. For example, in preparing the mesh comprising polypropylene, ifthe melting point of the degradable component is higher than that ofpolypropylene, the curing temperature of the mesh is determined on thebasis of the melting point of polypropylene, that is, the mesh may becured at 100 to 155° C. for 3 to 20 minutes.

In an embodiment of the present invention, a mesh having the followingtexture may be used by a flat warp knitting machine.

(The warp knitted texture Example 1)

The number of gauge=18 (Gauges/inch)

-   G1=10 01 10 12 21 12-   G2=00 11 00 22 11 22-   G=guide bar    (The warp knitted texture Example 2)    The number of gauge=12 (Gauges/inch)-   G1=10 01 10 12 21 12-   G2=00 11 00 22 11 22-   G3=00 11 00 22 11 22-   G4=00 11 00 11 00 11    (The warp knitted texture Example 3)    The number of gauge=12 (Gauges/inch)-   G1=10 01 10 12 21 12×4-   G2=00 11 00 22 11 22×4-   G3=22 33 22 33 22 33 11 22 11 11 00 11 11 22 11 33 22 33 22 33 22 44    33 44-   G4=11 22 11 33 22 33 22 33 22 44 33 44 22 33 22 33 22 33 11 22 11 22    00 22    (The warp knitted texture Example 4)    The number of gauge=18 (Gauges/inch)-   G1=10 12 23 21-   G2=23 21 10 12    (The warp knitted texture Example 5)    The number of gauge=18 (Gauges/inch)-   G1=21 12 10 12 21 23-   G2=12 21 23 21 12 10

FIG. 2A is an electronic microscopy image of the mesh according to thepresent invention before degradation, and FIG. 2B is that afterdegradation, showing that the component constituting the mesh has themonofilament form prior to degradation, and is converted to themultifilament form of several strands of the non-degradable polymerafter degradation.

In the present invention, the mesh is prepared with the monofilament inthe segmented pie form wherein the degradable polymer and thenon-degradable polymer are repeatedly and alternatively distributed inall directions throughout the whole fiber, to improve thebiocompatibility and the adhesive strength to the tissue in the body atthe early stage after performing the surgical operation. Further, thestiffness after degradation is reduced by at least 70% compared withthat before degradation, to maximize the flexibility of the meshremaining in the body after the surgical wound is healed. Compared withthe conventional mesh that contains only non-degradable components orpartially degradable components, in the present invention the initialand remaining amounts of the non-degradable components in the mesh arelowered, and simultaneously the biocompatibility and the flexibility ofthe mesh are improved.

Therefore, the mesh according to the present invention is suitable forhernia repair, since the mesh maintains the strength and the stiffnessto attain the convenience of the surgical operation at the early stage,and is partially degraded to improve the flexibility as the surgicalwound is healed.

According to the present invention, the monofilament with the segmentedpie structure formed by conjugated spinning of the degradable polymerand the non-degradable polymer may be applied to not only hernia mesh,but also to other operations, such as vaginal sling procedures,artificial ligament and tendon operations, fascial deficiencies whichrequire the add an reinforcing material or a bridging material, and thelike.

Hereinafter, the present invention will be more specifically describedby the following examples, which should not be understood to limit thescope of the invention.

EXAMPLE 1

The monofilament in the segmented pie form was prepared throughconjugated spinning of 55 vol % of a glycolide (75)/caprolactone (25)copolymer as a degradable polymer and 45 vol % of polypropylene as anon-degradable polymer under the conditions shown in the followingTable 1. The prepared monofilament in the segmented pie form was warpedwith 150 yarns/7″ beam to prepare the mesh according to the above warpknitted texture of Example 1. The prepared mesh was cured at 150° C. for5 minutes. The properties of the mesh, such as thickness, weight,tensile strength, and stiffness were determined according to theconventional measuring methods, and the results are shown in thefollowing Table 6. TABLE 1 glycolide (75)/ caprolactone Polymerpolypropylene (25) copolymer Melt index (g/10 min, 230° C.) 10 13Spinning Conditions Extruder Ext. 1 Ext. 2 The number of segments of thenon- 6 — degradable polymer Pre-pump pressure (kgf/cm²) 80 80Temperature in Zone 1 150 150 Extruder (° C.) Zone 2 160 165 Zone 3 170180 Zone 4 175 190 Zone 5 175 195 Temperature in Manifold (° C.) 180 198Temperature in Quantitative Pump 180 186 (° C.) Temperature in NozzlePack Die (° C.) 204 Capacity of Quantitative Pump 0.3 0.6 (cc/rev)Revolution speed of Quantitative 8.75 5.35 Pump (rpm) Temperature inCooling Bath (° C.) 25 Drawing Conditions First Roller velocity (m/min)6.7 First Drawing Oven Temperature (° C.) 70 Second Roller velocity(m/min) 47 Second Drawing Oven Temperature 100 (° C.) Third Rollervelocity (m/min) 55 Third Drawing Oven Temperature 140 (° C.) FourthRoller velocity (m/min) 46 Total Drawing Ratio 6.86 PreparationConditions of the Mesh Warping Conditions 150 yarns/7″ beam Warp KnittedTexture Warp Knitted Texture Example 1 Curing Conditions 150° C., 5minutes

EXAMPLE 2

The monofilament in the segmented pie form was prepared throughconjugated spinning of 55 vol % of a glycolide (75)/caprolactone (25)copolymer as a degradable polymer and 45 vol % of a propylene(97)/ethylene (3) copolymer as a non-degradable polymer under theconditions shown in the following Table 2. The prepared monofilament inthe segmented pie form was warped with 120 yarns/7″ beam to prepare themesh according to the above warp knitted texture of Example 2. Theprepared mesh was cured at 155° C. for 3 minutes. The properties of themesh, such as thickness, weight, tensile strength, and stiffness weredetermined according to the conventional measuring methods, and theresults are shown in the following Table 6. TABLE 2 Propylene (97)/ethylene (3) Glycolide (75)/ random caprolactone (25) Polymer copolymercopolymer Melt index (g/10 min, 230° C.) 8 12 Spinning ConditionsExtruder Ext. 1 Ext. 2 The number of segments of the non- 6 — degradablepolymer Pre-pump pressure (kgf/cm²) 80 80 Temperature in Zone 1 150 150Extruder (° C.) Zone 2 160 165 Zone 3 165 180 Zone 4 170 190 Zone 5 170195 Temperature in Manifold (° C.) 175 198 Temperature in QuantitativePump 175 186 (° C.) Temperature in Nozzle Pack Die 203 (° C.) Capacityof Quantitative Pump 0.3 0.6 (cc/rev) Revolution speed of Quantitative8.75 5.35 Pump (rpm) Temperature in Cooling Bath (° C.) 25 DrawingConditions First Roller velocity (m/min) 6.1 First Drawing OvenTemperature 70 (° C.) Second Roller velocity (m/min) 47 Second DrawingOven Temperature 100 (° C.) Third Roller velocity (m/min) 55 ThirdDrawing Oven Temperature 140 (° C.) Fourth Roller velocity (m/min) 46Total Drawing Ratio 7.54 Preparation Conditions of the Mesh WarpingConditions 120 yarns/7″ beam Warp Knitted Texture Warp Knitted TextureExample 2 Curing Conditions 155° C., 3 minutes

EXAMPLE 3

The monofilament in the segmented pie form was prepared throughconjugated spinning of 55 vol % of a dioxanone(90)/trimethylenecarbonate (9)/caprolactone (1) tri-block copolymer as adegradable polymer and 45 vol % of polypropylene as a non-degradablepolymer under the conditions shown in the following Table 3. Theprepared monofilament in the segmented pie form was warped with 120yarns/7″ beam to prepare the mesh according to the above warp knittedtexture of Example 3. The prepared mesh was cured at 95° C. for 10minutes. The properties of the mesh, such as thickness, weight, tensilestrength, and stiffness were determined according to the conventionalmeasuring methods, and the results are shown in the following Table 6.TABLE 3 Dioxanone (90)/ trimethylene- carbonate (9)/ caprolactone poly-(1) tri-block Polymer propylene copolymer Melt index (g/10 min, 230° C.)10 10 Spinning Conditions Extruder Ext. 1 Ext. 2 The number of segmentsof the non- 6 — degradable polymer Pre-pump pressure (kgf/cm²) 80 80Temperature Zone 1 150 150 in Zone 2 160 155 Extruder Zone 3 165 160 (°C.) Zone 4 165 160 Zone 5 165 160 Temperature in Manifold (° C.) 170 165Temperature in Quantitative Pump (° C.) 170 165 Temperature in NozzlePack Die (° C.) 175 Capacity of Quantitative Pump (cc/rev) 0.3 0.6Revolution speed of Quantitative Pump 8.75 5.35 (rpm) Temperature inCooling Bath (° C.) 25 Drawing Conditions First Roller velocity (m/min)5.8 First Drawing Oven Temperature (° C.) 70 Second Roller velocity(m/min) 45 Second Drawing Oven Temperature (° C.) 100 Third Rollervelocity (m/min) 53 Third Drawing Oven Temperature (° C.) 120 FourthRoller velocity (m/min) 42 Total Drawing Ratio 7.24 PreparationConditions of the Mesh Warping Conditions 120 yarns/7″ beam Warp KnittedTexture Warp Knitted Texture Example 3 Curing Conditions 95° C., 10minutes

EXAMPLE 4

The mesh was prepared by the same method as in Example 1, except thatthe number of the segments of the non-degradable polymer was 8. Theproperties of the prepared mesh, such as thickness, weight, tensilestrength, and stiffness were determined according to the conventionalmeasuring methods, and the results are shown in the following Table 6.

EXAMPLE 5

The mesh was prepared by the same method as in Example 1, except thatthe revolution speed (rpm) of the quantitative pump was 9.7 rpm for thepolypropylene (50 vol %) and 4.9 rpm for the glycolide/caprolactonecopolymer (50 vol %). The properties of the prepared mesh, such asthickness, weight, tensile strength, and stiffness were determinedaccording to the conventional measuring methods, and the results areshown in the following Table 6.

EXAMPLE 6

The mesh was prepared by the same method as in Example 1, except thatthe revolution speed (rpm) of the quantitative pump as 9.6 rpm for thepolypropylene (40 vol %) and 7.2 rpm for the glycolide/caprolactonecopolymer (60 vol %). The properties of the prepared mesh, such asthickness, weight, tensile strength, and stiffness were determinedaccording to the conventional measuring methods, and the results areshown in the following Table 6.

COMPARATIVE EXAMPLE 1

The mesh was prepared by the same method as in Example 1, except thatthe revolution speed (rpm) of the quantitative pump was 4.9 rpm for thepolypropylene (25 vol %) and 7.3 rpm for the glycolide/caprolactonecopolymer (75 vol %). The obtained monofilament was a sea/island type ofmonofilament wherein the polypropylene component was surrounded by theglycolide/caprolactone copolymer component as shown in FIG. 3A.

COMPARATIVE EXAMPLE 2

The mesh was prepared by the same method as in Example 1, except thatthe melt index of polypropylene was 27. The monofilament had thesegmented pie structure, but the tensile strength of the monofilamentwas poorer than that of Example 1, and the segmented pie structure wasnot symmetrical (FIG. 3B).

COMPARATIVE EXAMPLE 3

The mesh was prepared by the same method as in Example 1, except thatthe third roller velocity and the fourth roller velocity of the drawingconditions were made the same at 55 m/min such that no stress-relaxationwas applied.

The intensity of the obtained monofilament in the segmented pie form wasimproved compared with that of Example 1, but strand separation of thetwo components occurred when preparing the mesh (FIG. 3C).

COMPARATIVE EXAMPLE 4

The thickness, weight, tensile strength, and stiffness of a conventionalmesh product (Prolene Hernia mesh, Ethicon Co.) consisting of onlypolypropylene monofilament were measured according to the conventionalmeasuring methods. The results are shown in the following Table 6.

COMPARATIVE EXAMPLE 5

The thickness, weight, tensile strength, and stiffness of a conventionalmesh product (Vypro II Hernia mesh, Ethicon Co.) comprising aglycolide/lactide copolymer multifilament as a degradable component anda polypropylene monofilament as a non-degradable component were measuredaccording to the conventional measuring methods. The results are shownin the following Table 6.

EXPERIMENTAL EXAMPLE

The property measuring methods are summarized in the following Table 4.TABLE 4 Measuring Methods and Property Apparatuses Diameter, mm EPRegulation, Diameter Tensile strength, kgf EP Regulation, tensilestrength, Instron corporation

The property measuring methods are described in the following Table 5.

After measuring the initial properties, the properties of the mesh,wherein the degradable component was completely degraded underaccelerated conditions (80° C., 10 days in PBS, pH 7.4) and only thenon-degradable component remained, were measured, to compare theproperties before and after degradation. TABLE 5 Property MeasuringMethods and Apparatuses Thickness EP Regulation, Diameter (μm) Weight(g/m²) The weight of 10 cm × 10 cm mesh was converted on the basis ofm². Tensile 1″ × 6″ mesh was sampled in the horizontal and Strengthvertical directions in preparing the warp knitted texture, (Kgf/inch)and the tensile strength was measured by the tensile strength tester(Instron, 4204, U.S.SA.) wherein the sample was equipped with 50 mmtensile distance and tensed at 50 mm/min. Stiffness The mesh was cut toa 1″ × 1″ size, to measure (mgf) the stiffness by the stiffness tester(Gurley Precision Instrument, U.S.A.) after setting the load at 5 g andthe position at 2.

The measured properties of the mesh prepared in Examples 1 to 6 andComparative Examples 4 to 5 are shown in the following Table 6. TABLE 6Comparative Examples Examples Property 1 2 3 4 5 6 4 5 Property Diameter(μm) 150 145 140 150 150 200 150 100˜150 of Fiber Tensile Strength (Kgf)1 0.8 1.1 0.9 0.9 1.8 1 1˜2 Property Initial Thickness (μm) 550 540 540550 550 600 600 650 of Mesh Property Weight (g/m²) 64 62 60 64 64 80 8588 Tensile Vertical 20 18 21 18 20 22 26 20 Strength Horizontal 6 5 6 56 8 16 6 (Kgf) Stiffness Vertical 22 19 24 18 20 24 28 18 (mgf)Horizontal 10 9 12 9 10 11 25 10 Property Thickness (μm) 450 450 440 470470 420 600 470 after Weight (g/m²) 25 25 24 25 27 30 85 35 degradationTensile Vertical 12 9 8 10 13 12 26 12 Strength Horizontal 5 4 4 4 5 616 4 (Kgf) Stiffness Vertical 2 2 2 1.5 2 2 28 9 (mgf) Horizontal 1 0.80.5 0.5 1 0.5 25 2

As shown in Table 6, when comparing the properties of the mesh ofExamples 1 to 6, wherein the mesh was prepared with the monofilament inthe segmented pie form consisting of the degradable materials and thenon-degradable materials, with those of Comparative Example 4 to 5,wherein the mesh was prepared with only the non-degradable monofilamentor the mixture of the degradable multifilament and the non-degradablemonofilament, it is known that the initial properties of the mesh of thepresent examples were equal to those of the comparative examples, andthe remaining amount and the stiffness are relatively reduced comparedthereto, to improve the biocompatibility and the flexibility of thepresent inventive mesh.

That is, in the case of the conventional hernia mesh prepared with thepolypropylene monofilament as in Comparative Example 4, the initialstrength and the stiffness were maintained even after a certain time,while in the case of the mesh prepared as in Example 1, the degradablematerial was degraded and the amount remaining in the body was reducedto at least 3 times lower than that of Comparative Example 4, and thestiffness was reduced by at least 10 times to alleviate misfeelings ofthe patient.

Further, when comparing Examples 1 to 6 with Comparative Example 5, itis known that in Examples 1 to 6, the initial amount and the remainingamount after degradation is low, and the stiffness is lowered three tofour times, to remarkably improve the biocompatibility and theflexibility.

Comparative Example 1 is a case in which the content of polypropylene is30 vol % or less, showing that the monofilament obtained by conjugatedspinning does not have the segmented pie structure but rather has thesea/islands structure wherein the polypropylene component is surroundedby the glycolide/lactide copolymer component. When performing conjugatedspinning of two components with a big difference in the melt indexes asin Comparative Example 2, the component with the low melt index pushesthe component with the high melt index to one side at the distributingplate in the spinnerette, to generate the unequal segmented piestructure. Further, when applying no stress-relaxation at the lastheating stage of the drawing step as in Comparative Example 3, thestress is present between the fibers of the two components withdifferent thermal contractibilities, which generates the fiberseparation phenomenon when impacted from the outside, especially whenwarping and knitting while preparing the mesh.

As aforementioned, the present invention provides a useful technique forpreparing a mesh using a monofilament in a segmented pie structureobtained by conjugated spinning of a degradable polymer and anon-degradable polymer, to improve biocompatibility and flexibility.

1. A monofilament having a segmented pie structure formed by conjugatedspinning of a degradable polymer and a non-degradable polymer.
 2. Themonofilament according to claim 1, wherein the content of the degradablepolymer is 30 to 70 vol %, and the content of the non-degradable polymeris 30 to 70 vol %.
 3. The monofilament according to claim 1, wherein thedegradable polymer is a homopolymer or copolymer comprising one or moremonomers selected from the group consisting of glycolide, glycolic acid,lactide, lactic acid, caprolactone (ε-caprolactone), dioxanone(p-dioxanone), trimethylene carbonate, polyanhydride, andpolyhydroxyalkanoate (PHA).
 4. The monofilament according to claim 3,wherein the degradable polymer is a glycolide/caprolactone copolymer ora dioxanone/trimethylenecarbonate/caprolactone copolymer.
 5. Themonofilament according to claim 1, wherein the non-degradable polymer isselected from the group consisting of polyolefins, polyamides,polyurethanes, and fluoropolymers.
 6. The monofilament according toclaim 5, wherein the non-degradable polymer is polypropylene, or acopolymer of propylene and ethylene.
 7. The monofilament according toclaim 1, wherein the melt index of the degradable polymer is not lowerthan the melt index of the non-degradable polymer.
 8. The monofilamentaccording to claim 7, wherein the difference between the melt indexes ofthe degradable polymer and the non-degradable polymer is 10 or less. 9.The monofilament according to claim 1, wherein the non-degradablepolymer is divided into at least four strands.
 10. A method of using themonofilament according to claim 1 in hernia repair, vaginal slingprocedures, artificial ligament and tendon operations, or repairingfascial deficiencies that require addition of an reinforcing material ora bridging material.
 11. A hernia mesh having improved flexibility andbiocompatibility, comprising a monofilament having a segmented piestructure formed by conjugated spinning of a degradable polymer and anon-degradable polymer.
 12. The hernia mesh according to claim 11,wherein the content of the degradable polymer is 30 to 70 vol %, and thecontent of the non-degradable polymer is 30 to 70 vol %.
 13. The herniamesh according to claim 11, wherein the degradable polymer is ahomopolymer or a copolymer comprising one or more monomers selected fromthe group consisting of glycolide, glycolic acid, lactide, lactic acid,caprolactone (ε-caprolactone), dioxanone (p-dioxanone),trimethylenecarbonate, polyanhydride, and polyhydroxyalkanoate.
 14. Themonofilament according to claim 13, wherein the degradable polymer is aglycolide/caprolactone copolymer or adioxanone/trimethylenecarbonate/caprolactone copolymer.
 15. Themonofilament according to claim 11, wherein the non-degradable polymeris selected from the group consisting of polyolefins, polyamides,polyurethanes, and fluoropolymers.
 16. The monofilament according toclaim 15, wherein the non-degradable polymer is polypropylene, or acopolymer of propylene and ethylene.
 17. The monofilament according toclaim 11, wherein the melt index of the degradable polymer is not lowerthan the melt index of the non-degradable polymer.
 18. The monofilamentaccording to claim 17, wherein a difference between the melt indexes ofthe degradable polymer and the non-degradable polymer is 10 or less. 19.The monofilament according to claim 11, wherein the non-degradablepolymer is divided into at least four strands.
 20. The monofilamentaccording to claim 11, wherein the diameter of the monofilament is 100to 250 μm.
 21. The hernia mesh according to claim 11, wherein thestiffness of the degradable polymer after degradation is decreased atleast 70% compared with that before degradation.
 22. The hernia meshaccording to claim 11, wherein the non-degradable polymer is partitionedby the degradable polymer, and the degradable polymer has a continuousform.
 23. The hernia mesh according to claim 11, wherein the structureof the mesh is a square, hexagonal, or network structure.
 24. The herniamesh according to claim 11, wherein the pore size is 0.1 to 4.0 mm andthe thickness is 200 to 800 μm,
 25. The hernia mesh according to claim11, wherein the density is 8 to 20 gauges/inch based on the distancebetween the needles in a warp knitting machine.
 26. The hernia meshaccording to claim 11, wherein the degradable polymer is partially dyed.27. A method of preparing a hernia mesh, comprising the steps ofspinning, solidification, crystallization, and drawing to prepare amonofilament, and the steps of warping, knitting, and curing to preparethe hernia mesh, wherein: the spinning step is performed by melting 30to 70 vol % of a degradable polymer and 30 to 70 vol % of anon-degradable polymer, and conducting conjugated spinning to form asegmented pie structure; the drawing step is performed by applyingstress-relaxation to prepare the monofilament; and the curing step isperformed at 90 to 160° C. for 1 to 30 minutes.
 28. The method accordingto claim 27, wherein stress-relaxation of at least 10% is applied.